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Frequent biomass-burning activities occur in the Indo-China Peninsula in spring， and the aerosol generated will affect the atmospheric radiation budget of southwest China through the atmospheric circulation.Exploring its influence on the atmospheric heating rate can provide a basis for studying its influence on weather and climate.Based on the MERRA-2 reanalysis data of hourly aerosol and radiation flux under clear sky， their temporal and spatial characteristics were analyzed first.Secondly， using statistical methods such as EOF and synthetic analysis， the temporal and spatial evolution characteristics of aerosol optical thickness （AOD） and surface aerosol direct radiative forcing （ADRF） over the Indo-China Peninsula and their relationship with atmospheric shortwave heating rate were discussed.The results showed that： （1） During the biomass burning season from March to April， there was an extreme value of AOD in the Indo-China Peninsula and Yunnan Province.The time series trend also showed a high consistency.The central value of AOD in Laos and northern Vietnam was more than 1， and the AOD in Yunnan Province gradually increased from north to south due to its influence.（2） The high-value center of biomass combustion AOD in the Indo-China Peninsula from March to April was consistent with that of total AOD， indicating that it was mainly affected by biomass combustion aerosol at this time.The horizontal flux divergence of biomass burning aerosol is as high as 28 kg·m-1·d-1 in northern Laos， which can be transported northeast to China.（3） The spatial and temporal distribution of surface ADRF and AOD showed a high consistency.The high-value center of surface ADRF also existed in the northern part of Laos and Vietnam in March and April， and its value could reach -36 W·m-2.In the spatial distribution of the first mode of surface ADRF in EOF， the northeast corner of India bordering in Tibet of China， Laos， Vietnam and Thailand are all positive phase regions， with maximum values appearing from March to April.The extreme values decreased in 2017 and 2018 and increased again in 2019.The temporal variation trend of surface ADRF in Yunnan Province is consistent with that in the Indo-China Peninsula.（4） The statistical relationship between the negative surface ADRF and the atmospheric shortwave heating rate is as follows： The more the net radiant flux of the surface decreases， the greater the heating caused by the absorption of shortwave radiation by the lower atmosphere， indicating that the more the shortwave radiation flux trapped by the aerosol in the atmosphere， especially at 700 hPa in March and April.

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Numerous studies have shown negative health effects related to exposure to ambient particulate matter (PM), likely due to induced oxidative stress. In this study, we have examined ambient PM samples from Birr, a small (~5000 inhabitants) town in central Ireland, for their water-soluble DTT-based oxidative potential (OP_DTT) with a resolution of 6 h, together with online chemical characterization measurements, to assess the OP of organic aerosols, in particular from residential solid fuel burning. The OP_DTT normalized by the volume of sampled air shows a high variability, ranging from <0.1 to 3.8 nmol min−1 m−3, and a high correlation with PM mass. A lower variability was associated with the mass-normalized OP. Nevertheless, both tended to present higher values during night-time pollution episodes. Simple and multivariate linear regression approaches linked OP_DTT to residential solid fuel burning, and in particular to wood (~87%) and peat (~13%) combustion. The results of the present study show how residential solid fuel burning can have a severe impact on air quality, even in small towns, with potential negative health effects on the exposed population. [ABSTRACT FROM AUTHOR]

The vertical distribution of biomass burning aerosol (BBA) is important in regulating their impacts on weather and climate. The plume‐rise process affects the injection height of BBA and interacts with the air parcel lifting and cloud processes. However, these processes are not represented in most global climate models. In this study, we replaced the fixed vertical profiles of monthly BBA emissions in the Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1) with an interactive fire plume‐rise model. The vertical distribution of BBA emissions was calculated as a function of ambient thermodynamic conditions from the host E3SMv1, with distributions of fire sizes and sensible heat fluxes derived from the observations. The maximum fire radiative power (FRP) technique was used to determine the fire size. Scaling‐FRP technique is used to calculate the wildfire heat release. Daily BBA emission, superimposed with a fire diurnal cycle retrieved from the satellite observation, was included in model simulations. The model shows improved agreement with satellite retrievals and in situ measurement during the National Oceanic and Atmospheric Administration Wildfire Experiment for Cloud chemistry, Aerosol absorption, and Nitrogen campaign. The model‐observation comparison demonstrates the importance of the plume‐rise model and fire diurnal cycle assumption in determining the BBA fields. We also find that E3SMv1 with new features produces a larger carbonaceous aerosol burden, leading to 0.13 W m−2 warming at the top of atmosphere compared to the default E3SMv1. This highlights the importance of accurately representing the BBA injection height and indicates a no‐linear nature in the BBA‐induced radiative effect. Plain Language Summary: In this study, we replaced fixed vertical profiles of biomass burning aerosols (BBA) used in the default doe's Energy Exascale Earth System Model version 1 (E3SMv1) with an interactive fire plume‐rise model and fire diurnal cycle assumption. The BBA vertical profiles predicted by the model with the new features are in better agreement with the satellite observations and in situ aircraft observations compared to the default version. In addition, the inclusion of the plume‐rise model and fire diurnal assumption also lead to a warming effect as strong as 0.13 W m−2. Key Points: We incorporate an interactive fire plume‐rise model and fire diurnal cycle in the Energy Exascale Earth System Model version 1 (E3SMv1)The new features in E3SMv1 generate biomass burning aerosol vertical profiles that agree better with the observations than the default onesThe E3SMv1 with plume‐rise model and fire diurnal cycle causes a 0.13 W m−2 warming effect compared to the default one [ABSTRACT FROM AUTHOR]

Abstract The vertical distribution of biomass burning aerosol (BBA) is important in regulating their impacts on weather and climate. The plume‐rise process affects the injection height of BBA and interacts with the air parcel lifting and cloud processes. However, these processes are not represented in most global climate models. In this study, we replaced the fixed vertical profiles of monthly BBA emissions in the Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1) with an interactive fire plume‐rise model. The vertical distribution of BBA emissions was calculated as a function of ambient thermodynamic conditions from the host E3SMv1, with distributions of fire sizes and sensible heat fluxes derived from the observations. The maximum fire radiative power (FRP) technique was used to determine the fire size. Scaling‐FRP technique is used to calculate the wildfire heat release. Daily BBA emission, superimposed with a fire diurnal cycle retrieved from the satellite observation, was included in model simulations. The model shows improved agreement with satellite retrievals and in situ measurement during the National Oceanic and Atmospheric Administration Wildfire Experiment for Cloud chemistry, Aerosol absorption, and Nitrogen campaign. The model‐observation comparison demonstrates the importance of the plume‐rise model and fire diurnal cycle assumption in determining the BBA fields. We also find that E3SMv1 with new features produces a larger carbonaceous aerosol burden, leading to 0.13 W m−2 warming at the top of atmosphere compared to the default E3SMv1. This highlights the importance of accurately representing the BBA injection height and indicates a no‐linear nature in the BBA‐induced radiative effect.

Aerosol hygroscopicity plays a vital role in aerosol radiative forcing. One key parameter describing hygroscopicity is the scattering enhancement factor, f(RH), defined as the ratio of the scattering coefficient at humidified relative humidity (RH) to its dry value. Here, we utilize the f(80%) from ORACLES 2016 and 2018 airborne measurements to investigate the hygroscopicity of aerosols, its vertical distribution, its relationship with chemical composition, and its sensitivity to organic aerosol (OA) hygroscopicity over the South-East Atlantic (SEA) Ocean during the biomass burning (BB) season. We found that aerosol hygroscopicity remains steady above 2 km, with a mean f(80%) of 1.40±0.17. Below 2 km, aerosol hygroscopicity increases with decreasing altitude, with a mean f(80%) of 1.51±0.22, consistent with higher values of BB hygroscopicity found in the literature. The hygroscopicity parameter of OA (OA) is retrieved from the Mie model with a mean value of 0.11±0.08, which is in the middle to upper range compared to literature. Higher OA hygroscopicity is related to aerosols that are more aged, oxidized, and present at lower altitudes. The enhanced BBA hygroscopicity at lower altitudes is mainly due to a lower OA fraction, increased sulphate fraction, and greater OA at lower altitudes. We propose a parameterization that quantifies f(RH) with chemical composition and OA based on Mie simulation of internally mixed OA-(NH4)2SO4-BC mixture. The good agreement between the predictions and the ORACLES measurements implies that the aerosols in the SEA during the BB season can be largely represented by the OA-(NH4)2SO4-BC internal mixture with respect to the f(RH) prediction. The sensitivity of f(RH) to OA indicates that applying a constant OA is only suitable when the OA fraction is low and OA shows limited variation. However, in situations deviating these two criteria, OA can notably impact scattering coefficients and aerosol radiative effect; therefore, accounting for OA variability is recommended. [ABSTRACT FROM AUTHOR]

Numerous studies have shown negative health effects related to exposure to ambient particulate matter (PM), likely due to induced oxidative stress. In this study, we have examined ambient PM samples from Birr, a small (~5000 inhabitants) town in central Ireland, for their water-soluble DTT-based oxidative potential (OP_DTT) with a resolution of 6 h, together with online chemical characterization measurements, to assess the OP of organic aerosols, in particular from residential solid fuel burning. The OP_DTT normalized by the volume of sampled air shows a high variability, ranging from −1 m−3, and a high correlation with PM mass. A lower variability was associated with the mass-normalized OP. Nevertheless, both tended to present higher values during night-time pollution episodes. Simple and multivariate linear regression approaches linked OP_DTT to residential solid fuel burning, and in particular to wood (~87%) and peat (~13%) combustion. The results of the present study show how residential solid fuel burning can have a severe impact on air quality, even in small towns, with potential negative health effects on the exposed population.

Ångström exponents (α) allow reconstruction of aerosol optical spectra over a broad range of wavelengths from measurements at two or more wavelengths. Hyperspectral measurements of atmospheric aerosols provide opportunities to probe measured spectra for information inaccessible from only a few wavelengths. Four sets of hyperspectral in situ aerosol optical coefficients (aerosol‐phase total extinction, σext, and absorption, σabs; liquid‐phase soluble absorption from methanol, σMeOH‐abs, and water, σDI‐abs, extracts) were measured from biomass burning aerosols (BBAs). Hyperspectral single scattering albedo (ω), calculated from σext and σabs, provide spectral resolution over a wide spectral range rare for this optical parameter. Observed spectral shifts between σabs and σMeOH‐abs/σDI‐abs argue in favor of measuring σabs rather than reconstructing it from liquid extracts. Logarithmically transformed spectra exhibited curvature better fit by second‐order polynomials than linear α. Mapping second order fit coefficients (a1, a2) revealed samples from a given fire tended to cluster together, that is, aerosol spectra from a given fire were similar to each other and somewhat distinct from others. Separation in (a1, a2) space for spectra with the same α suggest additional information in second‐order parameterization absent from the linear fit. Spectral features found in the fit residuals indicate more information in the measured spectra than captured by the fits. Above‐detection σMeOH‐abs at 0.7 μm suggests assuming all absorption at long visible wavelengths is BC to partition absorption between BC and brown carbon (BrC) overestimates BC and underestimates BrC across the spectral range. Hyperspectral measurements may eventually discriminate BBA among fires in different ecosystems under variable conditions. Plain Language Summary: New measurement techniques for atmospheric aerosols are becoming available to obtain high spectral resolution optical information over a broad range of ultraviolet (UV)–visible–infrared wavelengths. Here, we measured UV‐visible spectra from aerosols emitted by five wildfires that exhibited curvature not adequately represented by a widely used single mathematical parameter known as the Ångström exponent. The observed spectral curvature differed across the five wildfires. We argue that the differences in absorption spectral curvature, in particular, were driven by different molecular composition of the smoke aerosols. We hypothesize that the observed curvature may eventually be used to optically differentiate wildfire aerosols and to better predict the optical and chemical evolution of wildfire smoke plumes downwind. We hope to encourage more routine measurements of this kind and to motivate development of improved measurement techniques and analytical approaches to maximize the information we can glean from such data. Key Points: Measured in situ atmospheric aerosol hyperspectral (<0.001 μm, resolution) optical properties in biomass burning plumes from 0.3 to 0.7 µmLog‐transformed spectra better fit by second‐order polynomials than Ångström exponents; measured spectra have details missed by fitsSpectral curvature in absorption driven by myriad organic chromophores over full wavelength range [ABSTRACT FROM AUTHOR]

Biomass burning (BB) emissions are one of the largest sources of carbonaceous aerosol, posing a significant risk as an airway irritant. Important BB markers include wood pyrolysis emissions, such as levoglucosan (LG) that is an anhydrous sugar bearing a six-carbon ring structure (i.e., 1,6-anhydro-β-D-glucopyranose). Atmospheric chemical aging of BB-derived aerosol (BBA) in the presence of nitrogen oxides (NO x ) can yield nitro-aromatic compounds, including 4-nitrocatechol (4NC). There is building evidence that NO x -mediated chemical aging of BBA poses a more serious exposure effect than primary pyrolysis emissions. This study provides a comparative toxicological assessment following the exposure to important BBA marker compounds in human lung cells (i.e., A549 and BEAS-2B) to determine whether aromatic 4NC is more toxic than BBA-bound anhydrous carbohydrate (i.e., LG). We determined inhibitory concentration-50 (IC 50 ) and examined reactive oxygen species (ROS) changes, mitochondrial dysfunction, and apoptosis induction in the two cell lines following exposure to LG and 4NC in a dose-response manner. In the BEAS-2B cells, estimated IC 50 values for 4NC were 33 and 8.8 μg mL -1 , and for LG were 2546 and ∼3 × 10 7  μg mL -1 at 24 h and 48 h of exposure, respectively. A549 cells exhibited a much higher IC 50 value than BEAS-2B cells. LG exposures resulted in mitochondrial stress with viability inhibition, but cells recovered with increasing exposure time. 4NC exposures at 200 μg mL -1 resulted in the induction of apoptosis at 6 h. Mitochondrial dysfunction and ROS imbalance induced the intrinsic apoptotic pathway induction following 4NC exposures. While increased ROS is caused by LG exposure in lung cells, 4NC is a marker of concern during BB emissions, as we observed apoptosis and high mitochondrial ROS in both lung cells at atmospherically-relevant aerosol concentrations. It may be associated with higher airway or inhalation pathologies in higher BBA emissions, such as wildfires or during wood combustion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

A bulk of evidence from in situ observations and lab experiments suggests that brown carbon (light-absorbing organic compounds in particles) can provide a significant yet highly variable contribution to the overall light absorption by aerosol particles from biomass burning (BB). Partly stemming from the complexity of the atmospheric evolution of organic aerosol (OA), the variability in brown carbon (BrC) absorption makes it difficult to partition the radiative effects of BrC and black carbon (BC) in atmospheric and climate models; as such, there are calls for satellite-based methods that could provide a statistical characterization of BrC absorption and its evolution in different regions of the world, especially in remote BB regions, such as Siberia. This study examined the feasibility of the statistical characterization of the evolution of BrC absorption and related parameters of BB aerosol in smoke plumes from intense wildfires in Siberia through the analysis of a combination of data from three satellite instruments: OMI (Ozone Monitoring Instrument), MISR (Multi-Angle Imaging SpectroRadiometer), and MODIS (Moderate Resolution Imaging Spectroradiometer). Using a Monte Carlo method, which related the satellite retrievals of the absorption and extinction aerosol optical depths to Mie theory calculations of the optical properties of BB aerosol, we found that the BrC absorption, as well as the imaginary refractive index for the OA, decreased significantly in Siberian BB smoke plumes during about 30 h of the daylight evolution, nevertheless remaining considerable until at least 70 h of the daylight evolution. Overall, the study indicated that the analysis of multi-platform satellite observations of BB plumes can provide useful insights into the atmospheric evolution of BrC absorption and the partitioning of BrC and BC contributions to the total light absorption by BB aerosol. [ABSTRACT FROM AUTHOR]

Biomass burning is a significant source of aerosol emissions in some regions and has a considerable impact on regional climate. Earth system model simulations indicate that increased biomass burning aerosol emissions contributed to statistically significant decreases in tropical precipitation over the 20th century. In this study, we use the Community Earth System Model version 1 Large Ensemble (CESM1-LENS) experiment to evaluate the mechanisms by which biomass burning aerosol contributed to decreased tropical precipitation, with a focus on South America and Southeast Asia. We analyze the all-but-one forcing simulations in which biomass burning aerosol emissions are held constant while other forcings (e.g., greenhouse gas concentrations) vary throughout the 20th century. This allows us to isolate the influence of biomass burning aerosol on processes that contribute to decreasing precipitation, including cloud microphysics, the radiative effects of absorbing aerosol particles, and alterations in regional circulation. We also show that the 20th century reduction in precipitation identified in the CESM1-LENS historical and biomass burning experiments is consistent across Coupled Model Intercomparison Project Phase 5 models with interactive aerosol schemes and the CESM2 single-forcing experiment. Our results demonstrate that higher concentrations of biomass burning aerosol increases the quantity of cloud condensation nuclei and cloud droplets, limiting cloud droplet size and precipitation formation. Additionally, absorbing aerosols (e.g., black carbon) contribute to a warmer cloud layer, which promotes cloud evaporation, increases atmospheric stability, and alters regional circulation patterns. Corresponding convectively coupled circulation responses, particularly over the tropical Andes, contribute to further reducing the flow of moisture and moisture convergence over tropical land. These results elucidate the processes that affect the water cycle in regions prone to biomass burning and inform our understanding of how future changes in aerosol emissions may impact tropical precipitation over the 21st century.

Absorbing aerosol from biomass burning impacts the hydrological cycle and radiation fluxes both directly and indirectly via modifications to convective processes and cloud development. Using the ICOsahedral Non‐hydrostatic modelling framework in a regional configuration with 1,500 m convection‐permitting resolution, we isolate the response of the Amazonian atmosphere to biomass burning smoke via enhanced cloud droplet number concentrations Nd (aerosol‐cloud interactions; ACI) and changes to radiative fluxes (aerosol‐radiation interactions; ARI) over a period of 8 days. We decompose ARI into contributions from reduced shortwave radiation and localized heating of the smoke. We show ARI influences the formation and development of convective cells: surface cooling below the smoke drives suppression of convection that increases with smoke optical depth, while the elevated heating promotes initial suppression and subsequent intensification of convection overnight; a corresponding diurnal response (repeating temporal response day‐after‐day) from high precipitation rates is shown. Enhanced Nd (ACI) perturbs the bulk cloud properties and suppresses low‐to‐moderate precipitation rates. Both ACI and ARI result in enhanced high‐altitude ice clouds that have a strong positive longwave radiative effect. Changes to low‐cloud coverage (ARI) and albedo (ACI) drive an overall negative shortwave radiative effect, that slowly increases in magnitude due to a moistening of the boundary layer. The overall net radiative effect is dominated by the enhanced high‐altitude clouds, and is sensitive to the plume longevity. The considerable diurnal responses that we simulate cannot be observed by polar orbiting satellites widely used in previous work, highlighting the potential of geostationary satellites to observe large‐scale impacts of aerosols on clouds. Plain Language Summary: There remain important uncertainties on how smoke from forest and grassland fires impacts the past, present, and future climates. In this study, we use a detailed model of the atmosphere over the Amazon rainforest to understand and quantify the processes by which smoke influences clouds and rain via two pathways: the first driven by changes to the absorption of solar radiation through the smoky atmosphere, and the second driven by an increase in the number of cloud droplets due to smoke particles. We find that the diurnal cycle of convection that drives much of the Amazon rainfall is greatly affected by changes to the radiation with less activity during the day and increasing activity overnight. The more numerous cloud droplets make the clouds brighter and help suppress rainfall rates. Changes to both radiation and cloud droplet number result in more extensive and thicker ice‐phase clouds that exert a warming effect on the climate; the longer the smoke plume persists for, the stronger the warming effect. Our findings highlight important processes that are not sufficiently represented in global climate models, and also highlight a need to use time‐resolved geostationary satellite observations of the region to capture more of the diurnal cycle. Key Points: Smoke drives strong diurnal responses in convection, cloud cover, and precipitation that cannot be observed by polar‐orbiting satellitesThe radiative effect of smoke is sensitive to plume longevity and the response of high‐altitude clouds that exert a strong positive effectSimulations suggest the localized suppression of convection scales with the optical depth of smoke over the Amazon rainforest [ABSTRACT FROM AUTHOR]

In September 2020, extremely strong wildfires in the western United States of America (i.e., mainly in California) produced large amounts of smoke, which was lifted into the free troposphere. These biomass‐burning‐aerosol (BBA) layers were transported from the US west coast toward central Europe within 3–4 days turning the sky milky and receiving high media attention. The present study characterizes this pronounced smoke plume above Leipzig, Germany, using a ground‐based multiwavelength‐Raman‐polarization lidar and the aerosol/cloud product of ESA's wind lidar mission Aeolus. An exceptional high smoke‐AOT >0.4 was measured, yielding to a mean mass concentration of 8 μg m−3. The 355 nm lidar ratio was moderate at around 40–50 sr. The Aeolus‐derived backscatter, extinction and lidar ratio profiles agree well with the observations of the ground‐based lidar PollyXT considering the fact that Aeolus' aerosol and cloud products are still preliminary and subject to ongoing algorithm improvements. Plain Language Summary: In September 2020, extremely strong wildfires in the western USA (i.e., mainly in California) produced large amounts of smoke. These biomass burning aerosol (BBA) layers were transported from the US west coast towards central Europe within 3‐4 days. This smoke plume was observed above Leipzig, Germany, for several days turning the sky milky and receiving high media attention ‐ it was the highest perturbation of the troposphere in terms of AOT ever observed over Leipzig. The first smoke plume arrived on 11 September 2020, just in time for a regular overpass of the Aeolus satellite of the European Space Agency (ESA). Aeolus accommodates the first instrument in space that actively measures profiles of a horizontal wind component in the troposphere and lower stratosphere. Aeolus has been launched to improve weather forecasts while assimilating the Aeolus wind profile data in near–real time. But Aeolus also delivers profiles of aerosol and cloud optical properties as spin‐off products. We performed a first assessment of the aerosol profiling capabilities of Aeolus while precisely analyzing the smoke plume above Leipzig with a ground‐based multiwavelength‐Raman‐polarization lidar. But we also show the dramatic impact of fires in the western USA on atmospheric conditions over central Europe. Key Points: Smoke from the extraordinary 2020 Californian wild fires traveled within 3–4 days toward EuropeHighest Aerosol Optical Thickness ever measured in the free troposphere over Leipzig, Germany, Central Europe, with ground‐based lidarUnique opportunity for a first assessment of the aerosol optical profiles of the spaceborne wind lidar mission Aeolus [ABSTRACT FROM AUTHOR]

A bulk of evidence from in situ observations and lab experiments suggests that brown carbon (light-absorbing organic compounds in particles) can provide a significant yet highly variable contribution to the overall light absorption by aerosol particles from biomass burning (BB). Partly stemming from the complexity of the atmospheric evolution of organic aerosol (OA), the variability in brown carbon (BrC) absorption makes it difficult to partition the radiative effects of BrC and black carbon (BC) in atmospheric and climate models; as such, there are calls for satellite-based methods that could provide a statistical characterization of BrC absorption and its evolution in different regions of the world, especially in remote BB regions, such as Siberia. This study examined the feasibility of the statistical characterization of the evolution of BrC absorption and related parameters of BB aerosol in smoke plumes from intense wildfires in Siberia through the analysis of a combination of data from three satellite instruments: OMI (Ozone Monitoring Instrument), MISR (Multi-Angle Imaging SpectroRadiometer), and MODIS (Moderate Resolution Imaging Spectroradiometer). Using a Monte Carlo method, which related the satellite retrievals of the absorption and extinction aerosol optical depths to Mie theory calculations of the optical properties of BB aerosol, we found that the BrC absorption, as well as the imaginary refractive index for the OA, decreased significantly in Siberian BB smoke plumes during about 30 h of the daylight evolution, nevertheless remaining considerable until at least 70 h of the daylight evolution. Overall, the study indicated that the analysis of multi-platform satellite observations of BB plumes can provide useful insights into the atmospheric evolution of BrC absorption and the partitioning of BrC and BC contributions to the total light absorption by BB aerosol.

The aim of this paper is to study the spatio-temporal evolution of a long-lasting Canadian biomass burning event that affected Europe in August 2018. The event produced biomass burning aerosol layers which were observed during their transport from Canada to Europe from the 16 to the 26 August 2018 using active remote sensing data from the space-borne system Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The total number of aerosol layers detected was 745 of which 42% were identified as pure biomass burning. The remaining 58% were attributed to smoke mixed with: polluted dust (34%), clean continental (10%), polluted continental (5%), desert dust (6%) or marine aerosols (3%). In this study, smoke layers, pure and mixed ones, were observed by the CALIPSO satellite from 0.8 and up to 9.6 km height above mean sea level (amsl.). The mean altitude of these layers was found between 2.1 and 5.2 km amsl. The Ångström exponent, relevant to the aerosol backscatter coefficient (532/1064 nm), ranged between 0.9 and 1.5, indicating aerosols of different sizes. The mean linear particle depolarization ratio at 532 nm for pure biomass burning aerosols was found equal to 0.05 ± 0.04, indicating near spherical aerosols. We also observed that, in case of no aerosol mixing, the sphericity of pure smoke aerosols does not change during the air mass transportation (0.05–0.06). On the contrary, when the smoke is mixed with dessert dust the mean linear particle depolarization ratio may reach values up to 0.20 ± 0.04, especially close to the African continent (Region 4).

In this work are presented results from recent intensive field measurements conducted in the Po Valley region in the frame of the EC-funded EUCAARI project, where state-of-the-art instruments were run in parallel in the joint effort to quantitatively apportion the primary and secondary fractions of the organic aerosols (OA) and their origins. We focused on the results obtained by applying factor analysis methodologies (i.e. positive matrix factorization, PMF) to spectroscopic data such as those produced by aerosol mass spectrometry (AMS) and nuclear magnetic resonance spectroscopy (NMR) while aiming at OA source apportionment.

We present on-line molecular composition measurements of wintertime particulate matter (PM) during 2014 using an iodide-adduct high-resolution, time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) coupled to a Filter Inlet for Gases and AEROsols (FIGAERO). These measurements were part of an intensive effort to characterize PM in the region with a focus on ultrafine particle sources. The technique was used to detect and quantify different classes of wood burning tracers, including levoglucosan, methoxyphenols, and nitrocatechols, among other compounds in near real-time. During the campaign, particulate mass concentrations of compounds with the same molecular composition as levoglucosan ranged from 0.002 to 19 μg/m 3 with a median mass concentration of 0.9 μg/m 3 . Wood burning markers, in general, showed a strong diurnal pattern peaking at night and in the early morning. This diurnal profile combined with cold, stagnant conditions, wind directions from predominantly residential areas, and observations of lower combustion efficiency at night support residential wood burning as a dominant source of wintertime PM in Port Angeles. This finding has implications for improving wintertime air quality in the region by encouraging the use of high efficiency wood-burning stoves or other cleaner home heating options throughout the relevant domain. [ABSTRACT FROM AUTHOR]

PM aerosol characterization on organic tracers for biomass burning (levoglucosan and its isomers and dehydroabietic acid) was conducted within the AERTRANS project. PM filters ( N = 90) were sampled from 2010 to 2012 in busy streets in the urban centre of Madrid and Barcelona (Spain) at ground-level and at roof sites. In both urban areas, biomass burning was not expected to be an important local emission source, but regional emissions from wildfires, residential heating or biomass removal may influence the air quality in the cities. Although both areas are under influence of high solar radiation, Madrid is situated in the centre of the Iberian Peninsula, while Barcelona is located at the Mediterranean Coast and under influence of marine atmospheres. Two extraction methods were applied, i.e. Soxhlet and ASE, which showed equivalent results after GC-MS analyses. The ambient air concentrations of the organic tracers for biomass burning increased by an order of magnitude at both sites during winter compared to summer. An exception was observed during a PM event in summer 2012, when the atmosphere in Barcelona was directly affected by regional wildfire smoke and levels were four times higher as those observed in winter. Overall, there was little variation between the street and roof sites in both cities, suggesting that regional biomass burning sources influence the urban areas after atmospheric transport. Despite the different atmospheric characteristics in terms of air relative humidity, Madrid and Barcelona exhibit very similar composition and concentrations of biomass burning organic tracers. Nevertheless, levoglucosan and its isomers seem to be more suitable for source apportionment purposes than dehydroabietic acid. In both urban areas, biomass burning contributions to PM were generally low (2 %) in summer, except on the day when wildfire smoke arrive to the urban area. In the colder periods the contribution increase to around 30 %, indicating that regional biomass burning has a substantial influence on the urban air quality. [ABSTRACT FROM AUTHOR]

Abstract: Biomass burning emits large amounts of aerosol particles globally, influencing human health and climate, but the number and size of the particles is highly variable depending on fuel type, burning and meteorological conditions, and secondary reactions in the atmosphere. Ambient measurements of aerosol during wildfire events can therefore improve our understanding of particulate matter produced from biomass burning. In this study, time-resolved sub-micrometer ambient aerosol size and mass distributions of freshly emitted aerosol were measured for three biomass burning wildfire events near Northridge, California, located in the highly populated San Fernando Valley area of Los Angeles. One fire (Marek) was observed during the dry Santa Ana conditions that are typically present during large Southern California wildfires, but two smaller fires (Getty and Camarillo) were observed during the more predominant non-Santa Ana weather conditions. Although the fires were generally small and extinguished quickly, they produced particle number concentrations as high as 50,000 cm−3 and mass concentrations as large as 150 μg cm−3, well above background measurements and among the highest values observed for fires in Southern California. Therefore, small wildfires can have a large impact on air quality if they occur near urban areas. Particle number distributions were lognormal, with peak diameters in the accumulation mode at approximately 100 nm. However, significant Aitken mode and nucleation mode particles were observed in bimodal distributions for one fire. Significant variations in the median diameter were observed over time, as particles generally became smaller as the fires were contained. The results indicate that it is likely that performing mass measurements alone could systematically miss detection of the smaller particles and size measurements may be better suited for studies of ambient biomass burning events. Parameters of representative unimodal and bimodal lognormal fits to the distributions are provided for reproduction of distributions in aerosol and climate models. [Copyright &y& Elsevier]

ABSTRACT El Niño/La Niña Southern Oscillation ( ENSO), Indian Ocean Dipole ( IOD) and aerosols have important roles to play in relation to Southeast Asian rainfall anomalies. This study investigates connections between these factors and local seasonal rainfall anomalies at 17 locations throughout Thailand using ground measurements and satellite observations available from 1980 to October 2011. This research investigates further the usefulness of incorporating these factors into rainfall forecasts. Results from canonical correlation analysis indicate that strong ENSO signals from October to March may affect rainfall anomalies in the nonsummer monsoon months, whereas IOD signals in the previous summer monsoon months were deemed to be of greater responsibility for current summer monsoon rainfall. Comparison of rainfall levels with different aerosol loadings suggests rainfall-decreasing aerosol from December to February for the South East Coast and in pre-summer monsoon months for deeper inland areas having less coastal influences. Rainfall-increasing aerosol was observed in post-summer monsoon months at the inland stations. The use of ENSO/ IOD signals as predictors yielded better rainfall forecast model performance than that of the aerosol loading. However, model performance significantly improved when both ENSO/ IOD signals and seasonal aerosol loadings were introduced. [ABSTRACT FROM AUTHOR]

Large sources of aerosol particles and their precursors are ubiquitous in East Asia. Such sources are known to impact the South China Sea (henceforth SCS), a sometimes heavily polluted region that has been suggested as particularly vulnerable to climate change. To help elucidate springtime aerosol transport into the SCS, an intensive study was performed on the remote Dongsha (aka Pratas) Islands Atoll in spring 2010. As part of this deployment, a Davis Rotating-drum Uniform size-cut Monitor (DRUM) cascade impactor was deployed to collect size-resolved aerosol samples at the surface that were analyzed by X-ray fluorescence for concentrations of selected elements. HYSPLIT backtrajectories indicated that the transport of aerosol observed at the surface at Dongsha was occurring primarily from regions generally to the north and east. This observation was consistent with the apparent persistence of pollution and dust aerosol, along with sea salt, in the ground-based dataset. In contrast to the sea-level observations, modeled aerosol transport suggested that the westerly flow aloft (∼700 hPa) transported smoke-laden air toward the site from regions from the south and west. Measured aerosol optical depth at the site was highest during time periods of modeled heavy smoke loadings aloft. These periods did not coincide with elevated aerosol concentrations at the surface, although the model suggested sporadic mixing of this free-tropospheric aerosol to the surface over the SCS. A biomass burning signature was not clearly identified in the surface aerosol composition data, consistent with this aerosol type remaining primarily aloft and not mixing strongly to the surface during the study. Significant vertical wind shear in the region also supports the idea that different source regions lead to varying aerosol impacts in different vertical layers, and suggests the potential for considerable vertical inhomogeneity in the SCS aerosol environment. [ABSTRACT FROM AUTHOR]

Abstract: Desorption electrospray ionization mass spectrometry (DESI-MS) technique was applied to the quantitative analysis of polycyclic aromatic hydrocarbons (PAHs) in biomass burning aerosols. Experimental conditions were optimized to enhance the detection efficiencies of PAHs. DESI-MS signal intensities showed good linear responses to the amount of PAHs in a dynamic range of four orders of magnitude and the detection limit is about 1pg/mm2. Mass concentrations of three-, four-, five-, six-ring PAHs in laboratory-made rice straw burning aerosols were directly measured by DESI-MS without any sample pretreatment. The results agree well with the parallel measurement by traditional GC–MS. DESI phenomenon was also observed for other compounds in biomass burning aerosols such as sugars, inorganic and organic acids. Potential applications of DESI-MS to the rapid analysis of multiple components in aerosol samples were discussed. [Copyright &y& Elsevier]

Abstract: A thermal extraction–two-dimensional gas chromatography–mass spectrometry (TE–GC–GC–MS) method with heart-cutting is developed for quantitatively assessing nitrogen (N)-bearing organic species (e.g., pyrrole, pyridine, nitriles, and amines) in aerosols emitted from agricultural fires. Pyrolysis of the constituents in the crop residue is a likely formation pathway for these compounds. An evaluation of the TE–GC–GC–MS method proficiency for them confirms low carryover (<1%), adequate recovery (84–100%), high reproducibility (<9% RSD), picogram method detection limits, and a linear dynamic range spanning four orders of magnitude. The 14 substances for which quantitative results are available are primarily heterocyclic aromatic N compounds that comprise 0.7% (w/w) of the total fine aerosol mass. The benefits of TE–GC–GC–MS versus conventional GC–MS methods for organic N species in aerosols may depend on the matrix and the target N analyte concentration in that matrix; for the biomass burning aerosol examined in this study, the former approach reduces the unresolved complex mixture and detects organic N species not seen with GC–MS. We show another advantage of TE–GC–GC–MS is that it adequately resolves the anhydro-sugar (e.g., levoglucosan), alkanoic acid, and substituted phenol molecules in the biomass burning aerosol without the use of methylation or trimethyl-silyl derivatizing agents. [Copyright &y& Elsevier]

Reactions of levoglucosan with $$ OH^{ \bullet } $$ produced from Fenton chemistry were studied in solution serving as a proxy for biomass burning aerosols. Two modes of oligomerization (≤2000 u) were observed for reaction times between 1 and 7 days using matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS) and laser desorption ionization time-of-flight mass spectrometry (LDI-TOF-MS). Single-mass unit continuum mass distributions with dominant −2 u patterns were measured and superimposed by a +176/+162 u oligomer series. This latter oligomer pattern was attributed to a Criegee rearrangement (+14 u) of levoglucosan, initiated by $$ OH^{ \bullet } $$ , forming a lactone (176 u). The acid-catalyzed reaction of any ROH from levoglucosan (+162 u) forms an ester through transesterification of the lactone functionality, whereupon propagation forms polyesters. Proposed products and chemical mechanisms are suggested as sources and precursors of humic-like substances (HULIS), which are known to possess a large saccharic component and are possibly formed from biomass burning aerosols (Andreae, Global Biomass Burning, MIT Press, Cambridge, Massachusetts, 3–21, ). [ABSTRACT FROM AUTHOR]

Abstract: The main objective of this study is to investigate the chemical characteristics of biomass burning aerosol and its impact on regional air quality during an agricultural waste burning period in early summer in the rural areas of Korea. A 12-h integrated intensive sampling of biomass burning aerosol in the fine and coarse modes was conducted on 2–20 June 2003 in Gwangju, Korea. The collected samples were analyzed for concentrations of mass, ionic, elemental, and carbonaceous species. Average concentrations of fine and coarse mass were measured to be 67.9 and 18.7 μg m−3 during the biomass burning period, 41.9 and 18.8 μg m−3 during the haze period, and 35.6 and 13.3 μg m−3 during the normal period, respectively. An exceptionally high PM2.5 concentration of 110.3 μg m−3 with a PM2.5/PM10 ratio of 0.79 was observed on 6 June 2003 during the biomass burning period. The potassium ratio method was used to identify biomass burning samples. The average ratio of potassium in the fine mode to the coarse mode (FK/CK) was 23.8 during the biomass burning period, 6.0 during the haze period, and 4.7 during the normal period, respectively. A FK/CK ratio above 9.2 was considered a criterion for biomass burning event in this study. Particulate matter from the open field burning of agricultural waste has an adverse impact on visibility, human health, and regional air quality. [Copyright &y& Elsevier]

Abstract: Simultaneous ground-based measurements of aerosol chemical composition and atmospheric aerosol optical depth (AOD) in the UV and visible regions were carried out at Gwangju (35.13°N, 126.50°E), Korea during a biomass burning period, October 4–November 12,2002. An Asian dust event and biomass burning events were observed during the study period. The correlation coefficients (R) between AOD and PM2.5 and PM10 mass concentration during the study period are 0.58±0.15 and 0.52±0.14, respectively. Aerosol optical properties (AOD and Ångström exponent) and chemical characteristics were presented for selected days and their impacts on aerosol loading were examined. Both fine and coarse mode particle mass concentrations increased on biomass burning day resulting in high AOD values. The simultaneous occurrence of Asian dust and biomass burning resulted in the highest AOD of 1.20 at 311nm and the lowest Ångström exponent of 0.42 in the visible range. When both transported urban pollutants and land dust aerosols affected the air quality over the study area, AOD and surface PM mass concentration increased 18–60% and 230–890%, respectively. [Copyright &y& Elsevier]

Abstract: We summarise the microphysical and optical parameters of some principal aerosol species obtained by instrumentation on the UK Met Office C-130 aircraft during international field campaigns since 1996. The aerosol species include Saharan dust, biomass burning aerosol, European continental pollution, eastern seaboard USA pollution, and clean maritime aerosol. The typical structure of the aerosol in the vertical from each airmass type is described. Microphysical parameters are described that comprise the mode radius and geometric standard deviation associated with 2–3 lognormal fits to the mean observed aerosol size distributions spanning the accumulation and coarse modes. Optical parameters comprising the aerosol single scattering albedo (which was both measured and derived from Mie theory), specific extinction coefficient, and asymmetry factor (which were derived from Mie theory) are also presented. Where available, evolution of the physical and optical properties of the aerosol has been highlighted. Comparisons with long-term ground-based AERONET aerosol retrievals show reasonable agreement. Our observations provide useful data for validating and improving global circulation models (GCMs) that use physically based aerosol representation and for validating satellite retrievals of the physical and optical properties of aerosols. [Copyright &y& Elsevier]

Biomass burning (BB) emissions significantly deteriorate air quality in many regions worldwide, impact human health and perturbing Earth's radiation budget and climate. South America is one of largest contributors to BB emissions globally. After Amazonia, BB emissions from open and agricultural fires of Northern South America (NSA) are the most significant. Recent evidence shows a strong correlation between fire counts in NSA and Brown Carbon in some Colombian cities, suggesting a substantial seasonal contribution of regional BB sources to air pollution levels in the densely populated areas of NSA. In this work we use the atmospheric regional chemical transport model WRF-Chem to assess the contribution of open BB events to pollutant concentration and to estimate potential health impacts associated with wildfire events in NSA. Three nested domains are used to simulate atmospheric composition in the Northern part of South America and the Caribbean. Simulations included biogenic and anthropogenic emissions from a global emission inventory merged with local emissions for the city of Bogotá. Two modelling scenarios were considered, a base case without BB emissions (NO_FIRE) and a sensitivity scenario with BB emissions. Simulations were carried out for periods of strong BB activity in NSA. In the NO_FIRE scenario, aerosol concentrations are unrealistically low. When BB emissions are is included background PM 2.5 concentrations increase 80%. The increment in aerosol concentrations is mainly driven by Secondary Organic Aerosols. In the case of Bogotá, the most densely populated city in the domain, monthly mean increase in PM 2.5 is 3.3 μg m−3 and 4.3 ppb for O 3. Modeled meteorological and air pollution fields are in better agreement with observations when high spatial resolution (3 × 3 km) is used in the simulations. The total estimated short-term all-cause mortality associated to BB during February in the region is 171 cases, 88 PM 2.5 -related and 83 O 3 -related mortality. Unlabelled Image • We used WRF-Chem to model the transport of Biomass Burning plumes in Northern South America. • Regional aerosol background concentrations are dominated by biomass burning during the dry season. • SOA contributes a substantial fraction of biomass burning smoke in the region. • Regional Ozone background levels are strongly impacted during the Biomass burning season. • Nearly 170 excess deaths can be associated with biomass burning PM2.5 and O3 increases during February, often the most affected by fires. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the spatio-temporal evolution of a long-lasting Canadian biomass burning event that affected Europe in August 2018. The event produced biomass burning aerosol layers which were observed during their transport from Canada to Europe from the 16 to the 26 August 2018 using active remote sensing data from the space-borne system Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The total number of aerosol layers detected was 745 of which 42% were identified as pure biomass burning. The remaining 58% were attributed to smoke mixed with: polluted dust (34%), clean continental (10%), polluted continental (5%), desert dust (6%) or marine aerosols (3%). In this study, smoke layers, pure and mixed ones, were observed by the CALIPSO satellite from 0.8 and up to 9.6 km height above mean sea level (amsl.). The mean altitude of these layers was found between 2.1 and 5.2 km amsl. The Ångström exponent, relevant to the aerosol backscatter coefficient (532/1064 nm), ranged between 0.9 and 1.5, indicating aerosols of different sizes. The mean linear particle depolarization ratio at 532 nm for pure biomass burning aerosols was found equal to 0.05 ± 0.04, indicating near spherical aerosols. We also observed that, in case of no aerosol mixing, the sphericity of pure smoke aerosols does not change during the air mass transportation (0.05–0.06). On the contrary, when the smoke is mixed with dessert dust the mean linear particle depolarization ratio may reach values up to 0.20 ± 0.04, especially close to the African continent (Region 4). [ABSTRACT FROM AUTHOR]